This subject never dies no matter what, so I'm going to lay this all out there for the guys who haven't but want to run a BHAF. There seems to be a lot of institutional inertia out there that says you can just remove the air box, jam a BHAF in there, and call it a day.
THIS IS WRONG.
The BHAF requires some simple, but important additional measures to ensure reliable performance and long service life. I have seem some BHAF installs that looked professional. I have seen very many that looked inattentive to detail. I have even seen some that were splendid examples of straight-up bad judgement. I will show you the things to do, and more importantly, the things to not
do when installing a BHAF.
This write-up was made possible by Black Toad Distinctive Dark Ale:
I have two scenarios for you, with an optional mod at the end.
Scenario 1: Without a Heat Shield
The first scenario assumes you are not
running a heat shield. We will start at the point where the stock air box has been removed and you think you're ready to install the BHAF. Hold your horses, Chuck. We got some business to take care of. This is what you will see, the airbox mounting studs sticking up out of the fender:
Some seem to think that you can just let the filter rest on these studs and nothing bad will ever happen. This is not true. Worse yet, I actually saw a thread where a guy suggested smashing the filter onto these studs so they could help hold the filter in place. I cannot articulate how stupid this is. As the filter sits there and vibrates, the studs will tear holes in the filter media, at which point you might as well not even have the filter. The filter needs to be protected from these studs.
First, you want to spread a soft, flexible material over the exposed fender. I chose to use an extra piece of toolbox drawer liner, folded over on itself (two layers), but pretty much anything similar to this will fit the bill. Press this down over the studs so the studs keep it from sliding off the fender.
You still have a problem though, and the problem is the studs. The best way to get around this without removing them is to press short lengths of fuel hose over the studs. The size is 3/16" or 1/4", I forget, but it should press on by hand and not come off the stud without a fight.
This will protect the filter sufficiently well. I ran mine like that for about a year (15k or so) and when I took it out, you couldn't even tell where the studs were touching it.
The next thing you need to do is test-fit the filter and see what it can
move around and hit. The two A/C lines are the primary concerns here. If your filter is in danger of hitting either, slit a short piece of 1/2" fuel/heater line lengthwise and slip it around the A/C lines. I'll show a picture of this later. It's important not only to protect the filter, but to protect the lines. I have seen pictures of lines that actually failed from the BHAF rubbing on them.
Finally, we're almost done. The last thing needed is to support the neck of the filter. Not all BHAFs are created equal. Each brand has it's own level of quality, and one place this is most apparent is in the base material. What I mean is the rubbery, plasticy black part that isn't the media or the wire mesh. On some brands, this stuff is very flexible and closer to a soft rubber. The base material on my Donaldson is fairly solid, almost a plastic, but not quite.
In the original application, the filter outlet is designed to slip over a piece of 4" pipe. The filter itself is then retained in place by an airbox lid. The filter outlet was never designed to have a hose clamped to it.
Doing so, without properly supporting the outlet, will eventually deform it and allow unfiltered air to leak into the turbo inlet tube. Supporting the neck is relatively easy:
Inside the neck of my filter is a 1-3/8" long piece of 4" exhaust pipe, painted black so it won't rust. That's all you have to do. Now, you could attach the turbo inlet tube with a t-bolt clamp if you wanted, and it will never crush, deform, or leak once the clamp is tightened.
You're done. Put everything together and crack a Black Toad.
Scenario 2: With a Heat Shield
The second scenario assumes you are using a heat shield. This scenario shares some common elements with the first scenario. You need to support the neck of the filter, no matter what. You also need to protect the filter from mechanical damage, but the way we do that is slightly different.
The airbox studs on my truck were fairly mangled by the time I got to doing this writeup, and are not suitable for re-use. If yours are okay, just install your heat shield to the studs using acorn nuts of whatever thread size they are, I'm assuming M6x1 but check for yourself. If you're like me and need to remove the studs, you have to pull your fender liner out. There are 9 clips, use a body clip puller because a screwdriver is a royal headache. Make sure you have a box of these on hand to replace the clips you just destroyed:
Once the fender liner is out, you get a gander at the stud bases:
They are a nut-sert type deal, but I'm assuming the stud and the insert is one piece because I couldn't get any of mine to unthread from the insert. Remove them with a backflipping angle grinder attack.
This is what you're left with, holes that will give a loose fit for an 8mm bolt:
I used M8x20 flange bolts and flange locknuts, but grab a couple 25mm long ones just in case. You may need to use washers to shim the heat shield up on the two inboard bolts to keep the heat shield off the shock tower.
Here is the heat shield installed. Notice that I used acorn nuts:
This is what I was talking about on the A/C lines earlier:
You can use a few zip screws to secure your soft material to the floor of the heat shield, like so:
Optional: Install your Filter Minder
I love gauges. I would have gauges on my gauges if I could.
So, I took the opportunity to reinstall the stock filter minder on my BHAF. I have seen plenty of people that install it in the end of BHAF with the stock grommet, just drilling an appropriately sized hole. This isn't how it worked out with my Donaldson.
I measured the smallest diameter of the grommet, and it was just below 3/4" so I drilled an 11/16" hole in the filter end. Turns out the end on this filter is about 5/8" thick.
I tried countersinking the top of the hole, but I didn't have one big enough. Then I tried drilling it out some more, but it was just too thick for the grommet.
It turns out the stud that the grommet rides on unscrews from the filter minder. That's why there's a hex in it, use a 5mm allen wrench to remove it, and the filter minder itself has a female 1/8" NPT port.
At this point, I had a big ragged hole in my (still perfectly usable) filter, and a good NPT port in the filter minder. I said 'screw it' and went with a brass bulkhead fitting:
I ended up going with a 1/4" NPT bulkhead fitting with a 1/4" to 1/8" NPT reducer nipple because the OD of the threads was the right size for the hole I had already drilled. If you're doing this on purpose, there is no reason to not use a 1/8" NPT bulkhead fitting with a regular hex nipple. I did face the fitting down in the lathe so the shank end was flush with the nut when installed. This was just for aesthetic purposes, it's not required.
I installed the fitting with the nut on the outside, so that if it were to come apart, the filter minder would prevent the fitting from falling out of the hole. Otherwise, the nut could fall off and make it's way into my precious FMW.
See, it's far too pretty for that.
The filter minder installed:
And how it looks in the truck:
Now, in about 500 years, I'll know when my filter needs replacement.